The present invention relates to developer compositions for lithographic printing plates. More particularly, the invention relates to developers for printing plates of the so-called positive type which are sensitized with o-quinone diazide photosensitive materials.
It is known that the diazo groups of o-quinone diazides are removed by irradiation to actinic light, and that the compound itself changes to a compound with a carboxyl group. When the photosensitive coating containing o-quinone diazide is exposed to the light and developed with an alkaline developer, the part exposed to light is removed while the part not exposed to light remains as the image. Because of this characteristic, it is known as a positive-type photosensitive component for printing plates or for photoresist compositions. Compositions of o-quinone diazide are usually mixed with alkali-soluble resins having economical and practical advantages in such uses. Mixtures of phenol formaldehyde resins, or cresol formaldehyde resins, are generally used as the alkali soluble resins. Trisodium phosphate, sodium hydroxide, or sodium silicate alone, or their mixed aqueous solutions are used as a developer for sensitive films containing these o-quinone diazides. However, aqueous solutions of these developers tend to have detrimental etching effects on such printing plate substrate metals as aluminum. Also, the results of development vary considerably. In extreme cases, even a slight excess of developing time causes failure in image formation. If alkalinity is decreased, development speed decreases unacceptably. If alkalinity is increased, the aluminum or aluminum oxide substrate etches away, thus undesirably undermining and removing image as well as non-image areas.
Japanese Pat. No. 75-51324 suggests one method of attacking this problem. It teaches the addition of both an anionic and a dipolar surfactant to the aqueous alkaline developer solution.
Surfactants have also been used in other types of developers. U.S. Pat. No. 3,891,438 teaches the development of negative working printing plates sensitized by diazonium salts with aqueous solutions of organo-lithium salts to which anionic, cationic or non-ionic surfactants have been added.